Ireland's performance was noticeably lacking in some areas, particularly during the first half at Sydney's Allianz Stadium where Australia ran in four tries inside the opening 27 minutes.
The 10-12-13 axis of Carter Gordon, Len Ikitau, and Joseph-Aukuso Sua'ali'i led what was a rampaging Australian attack at times, much improved from November's record 46-19 defeat in Dublin.
However, Andy Farrell's charges displayed their battling qualities to cut a 12-point gap to 24-19 by half-time, as Jamison Gibson-Park added a slickly-crafted late try to scores from Cian Prendergast and Josh van der Flier.
Farrell was much happier with what his side produced after the break, as they outscored the Wallabies, who are without a win since last October, by two tries to one.
They had five attacking 22-metre entries in the second half, compared to one for the hosts, and they showed their experience to wear down the defence for Thomas Clarkson's all-important 77th minute try.
That made it 31-all, and Sam Prendergast succeeded in splitting the posts with the conversion from the left. Ben Donaldson had a long-range penalty opportunity right at the death, but missed the difficult kick.
A maximum haul was certainly the desired start to the inaugural Nations Championship, but the manner of the performance leaves Ireland with a good deal to work on heading into next Saturday's clash with Japan in Newcastle.
Speaking after what was one of the hardest earned victories of his Ireland coaching tenure, Farrell said: "That was a hell of a game, wasn't it? Especially for the neutral. Some fantastic tries. Australia, I thought they were awesome in the first half.
"We needed to come to the party a little bit more, and I think we did that after the break. Had them under a little bit of pressure - couldn't really convert it.
"But, wow, there were some big moments for us. Hugo Keenan's tackle there (on Sua'ali'i), you know. He deserves something special when you're fighting like that.
"And obviously Sam Prendergast, to have the calmness about him to convert that try. There were some big moments in that game."
The lead changed seven times across the 80-plus minutes in the New South Wales state city, and a vital spell just before half-time saw Keenan save one try, and Gibson-Park then use a Jack Conan pass to score from the edge of the Australian 22.
The momentum definitely swung in Ireland's favour at that stage, as the Green and the Gold, for all of their incisive attacking and collision-winning phases, were only five points to the good.
The clock was in the red when Sam Prendergast, Tadhg Furlong, Garry Ringrose, and Conan knitted together the crisp passing move which paved the way for Gibson-Park to dive in beside the posts.
Asked about that decision to play on and run the ball from the preceding scrum, rather than close out the half by kicking to touch, Farrell replied: "They believe in themselves, that if everyone's involved and we've got all 15 involved in our attack, then we can make things happen.
"I mean, the last thing we wanted to do is kick the ball away because we want to give ourselves a chance to do what we know we can do. So that was the most pleasing thing about it - the ambition to do what they know they're good at.
"That's what we pride ourselves on. Everyone being involved, everyone being an option, everyone working hard to make sure that we're able to make things work as a group. And we certainly was on that occasion.
"So it was a nice reference of what to do. There's a couple of 'what not to do' as well - with our carries and stuff like that in the first half.
"I thought that Australia won some key moments collision-wise and slowed our ball down, so there was plenty to fix."
There was added satisfaction for the Ireland coaches as while the team collectively failed to reach the heights of earlier in the year, they still found a way to win against opponents who produced some of their best attacking play in recent memory.
The Triple Crown winners proved stronger when the game became more attritional, tipping the arm wrestle in their favour with the terrific Conan standing out at number 8, making 16 carries, and a total of 18 tackles from as many attempts.
Backing up Dan Sheehan's leadership as he captained his country for the third time, the fit-again Tadhg Beirne had an important cameo that lasted half an hour, and saw him take over the captaincy for the tense finale.
Van der Flier led the tackle count with 19 during a typically busy 51 minutes on the pitch, while Stuart McCloskey kept up his eye-catching spring form, making almost 50 metres from eight carries, and beating four defenders.
A word for his Ulster colleague, Tom O'Toole, who emptied the tank as he carried 10 times, contributed 13 tackles, and had a positive day scrum wise, albeit that he came under pressure after having to come back on for the injured Jeremy Loughman.
Returning full-back Keenan earned plenty of plaudits as Ireland's player-of-the-match and a defensive talisman, his superb coverage of the back-field thwarting Australia twice in try-scoring situations.
In attack for the visitors, he was third for post-contact metres with 33.6 metres, and took a smart line onto a short Ringrose pass to get past Max Jorgensen for his try.
Happy to come out on the right side of a tight result, Farrell explained: "We talk about character the whole time. About how you're going to make each other feel, and not just that, the thousands of Irish that are here, living in Sydney, etc.
"How you're going to make them feel, leading up to the World Cup next year. It's a good night for us. That was a hell of a Test match.
To come out on the other side of it, it's very pleasing because Australia played really well.
"I suppose it's a good one for us because there's plenty to fix and we need to fix it properly for what's coming ahead, including next week.
"So, it's a good place to be fixing stuff and, earning a hard-fought win at the same time.
"But again, the positive is coming away with a big 'W' and fixing on the run. The tour is underway now."
Coming through an experience like today is sure to quicken the international development of the likes of Cian Prendergast, who marked his fourth start with his third try, and Nick Timoney, a lively presence off the bench with eight carries and four defenders beaten.
There are five uncapped players in the wider squad who will hope to push for inclusion against the Japanese, who started their summer run on a high by beating Italy (27-10) for the first time since 2018.
The Ireland boss admitted: "Obviously you'd love continuity (from the Six Nations), but within our season internationally, there's breaks all over the place.
"It's not like you guys in the Southern Hemisphere where you get a six-month block. But we've been together for a while, so we tend to regroup pretty quickly.
"The best thing about today is that we got over the line in a big Test match. But there's plenty to do, plenty to fix, plenty to get better at, and we've got Japan in Newcastle next week.
"This whole block, this whole experience coming to the Southern Hemisphere, half of our squad have never been here before, so it's priceless for what's coming ahead."
